Seghers prepared for his missions at the American College of Louvain (Leuven), Belg., was ordained in 1863, and soon embarked for the diocese of Vancouver Island, B.C. He interrupted his work there to attend the First Vatican Council (1869–70) as theologian to his bishop, Modeste Demers, whom he succeeded in 1873. Seghers in 1878 was appointed assistant to the archbishop of Oregon City, Ore., whose diocese included Oregon, Idaho, Montana, and northern California.

Three years later he became archbishop of Vancouver Island. His immediate task was to strengthen the Roman Catholic school system there. In 1883 he journeyed to Rome with other American archbishops to plan the proposed third Plenary Council of Baltimore, which helped develop the parochial school system in the United States. While he was in Rome, the see of Vancouver Island became vacant, and Seghers’ offer to return there was accepted in 1885. During a visit to Alaska the following year, he was murdered by a demented companion.